A polarization control module such as an optical isolator in the analytical medical field or other technical fields using a high-energy laser has recently been required to fully cope with incidence of high power light. The reason comes from the fact that when light possessing large power such as of 730 nm to 800 nm or 1000 nm to 1200 nm in the near-infrared wavelength range enters into the optical isolator using garnet crystal for Faraday rotator having a function of rotating polarization of light, the optical property of a Faraday rotator is disadvantageously caused to deteriorate due to elevation in heat produced by light absorption in the aforementioned garnet crystal.
To achieve a solution to the conventional problem as described above, there have been proposed a high-power optical isolator in Japanese Published Unexamined Application HEI 7-281129(A1), a short-wavelength high-power optical Isolator in Japanese Published Unexamined Application No. 2005-25138(A1), and an optical isolator in Japanese Published Unexamined Application No. 2005-43853(A1).
A heat-dissipating structure in the short-wavelength high-power optical Isolator (referred to as “Conventional Art 1”) disclosed in Japanese Published Unexamined Application No. 2005-25138(A1) will be described hereinafter as one example.
A cylindrical magnet and ring-shaped heat sink in this conventional heat-dissipating structure are housed within a case, bringing their outer peripheries in contact with the inner periphery of the case. The Faraday rotator is disposed in the cylindrical magnet. The Faraday rotator has one side or both sides secured on one side of the aforementioned heat sink, and the heat sink has the aforementioned one side secured on the side surface of the aforementioned magnet. In the short-wavelength high-power optical Isolator, when high power light enters the Fadaday rotator, the Faraday rotator produces heat by light absorption in an optical signal transmissive part of the rotator, allowing the heat thus produced to radiate to the magnet through the heat sink. Thus, the aforementioned Faraday rotator in the short-wavelength high-power optical Isolator is attained to increase its heat dissipation efficiency and restrain temperature elevation.
Next, the heat-dissipating structure (hereinafter referred to as “Conventional Art 2”) described in Japanese Published Unexamined Application No. 2005-43853(A1) will be described. The Faraday rotator in this heat-dissipating structure is disposed within a cylindrical magnet in an external holder. The both side surfaces of the Faraday rotator come in a heat transfer member of sapphire crystal. A void part between the inner periphery of the magnet and the outer peripheries of the Faraday rotator and the heat transfer member is filled with filler having thermal conductivity. In this conventional optical isolator, when high power light enters the Fadaday rotator, the Faraday rotator produces heat by light absorption in an optical signal transmissive part of the rotator, allowing the heat thus produced to radiate from the heat transfer member to the magnet through the filler and then be transmitted from the outer periphery of the magnet to the inner periphery of the external holder.
The aforementioned Conventional Art 1 and Conventional Art 2 have the following problems.
That is, the aforementioned Conventional Art 1 disadvantageously has the heat sink in direct contact with the magnet. Also, the aforementioned Conventional Art 2 has the filler in direct contact with the magnet. Thus, the heat produced by light absorption in the optical signal transmissive part of the Faraday rotator in the respective Conventional Art 1 and Conventional Art 2 is transferred to the magnet. Specifically, when the produced heat is high in temperature, the high-temperature heat causes the magnetic field of the magnet to decrease, consequently to subject to affect the function of the optical isolator. Furthermore, the heat produced in the optical isolator is released there in the optical isolator, thus to thermally affect the elements of the optical isolator, so the optical isolator has required improvement to optical characteristics.
The present invention seeks to provide a heat-dissipating structure for an optical isolator capable of suppressing an increase in temperature of a Faraday element without affecting the function of the optical isolator and gaining stable characteristics.